Deep gate-all-around semiconductor device having germanium or group iii-v active layer

ABSTRACT

Deep gate-all-around semiconductor devices having germanium or group III-V active layers are described. For example, a non-planar semiconductor device includes a hetero-structure disposed above a substrate. The hetero-structure includes a hetero-junction between an upper layer and a lower layer of differing composition. An active layer is disposed above the hetero-structure and has a composition different from the upper and lower layers of the hetero-structure. A gate electrode stack is disposed on and completely surrounds a channel region of the active layer, and is disposed in a trench in the upper layer and at least partially in the lower layer of the hetero-structure. Source and drain regions are disposed in the active layer and in the upper layer, but not in the lower layer, on either side of the gate electrode stack.

TECHNICAL FIELD

Embodiments of the invention are in the field of semiconductor devicesand, in particular, deep gate-all-around semiconductor devices havinggermanium or group III-V active layers.

BACKGROUND

For the past several decades, the scaling of features in integratedcircuits has been a driving force behind an ever-growing semiconductorindustry. Scaling to smaller and smaller features enables increaseddensities of functional units on the limited real estate ofsemiconductor chips. For example, shrinking transistor size allows forthe incorporation of an increased number of memory devices on a chip,leading to the fabrication of products with increased capacity. Thedrive for ever-more capacity, however, is not without issue. Thenecessity to optimize the performance of each device becomesincreasingly significant.

In the manufacture of integrated circuit devices, multi-gatetransistors, such as tri-gate transistors, have become more prevalent asdevice dimensions continue to scale down. In conventional processes,tri-gate transistors are generally fabricated on either bulk siliconsubstrates or silicon-on-insulator substrates. In some instances, bulksilicon substrates are preferred due to their lower cost and becausethey enable a less complicated tri-gate fabrication process. In otherinstances, silicon-on-insulator substrates are preferred because of thereduced leakage they can offer.

On bulk silicon substrates, the fabrication process for tri-gatetransistors often encounters problems when aligning the bottom of themetal gate electrode with the source and drain extension tips at thebottom of the transistor body (i.e., the “fin”). When the tri-gatetransistor is formed on a bulk substrate, proper alignment is needed foroptimal gate control and to reduce short-channel effects. For instance,if the source and drain extension tips are deeper than the metal gateelectrode, punch-through may occur. Alternately, if the metal gateelectrode is deeper than the source and drain extension tips, the resultmay be an unwanted gate capacitance parasitics.

Many different techniques have been attempted to reduce junction leakageof transistors. However, significant improvements are still needed inthe area of junction leakage suppression.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a cross-sectional view of a germanium-basedsemiconductor device having a bottom gate isolation (BGI) structure forleakage suppression.

FIG. 2 illustrates a cross-sectional view of a semiconductor devicehaving a germanium active layer with a deep gate-all-around structure,in accordance with an embodiment of the present invention.

FIG. 3A illustrates a schematic top-down views of a non-planarsemiconductor device having a germanium active layer and a deep gateall-around structure, in accordance with an embodiment of the presentinvention.

FIG. 3B illustrates a schematic cross-sectional view of the non-planarsemiconductor device of FIG. 3A, in accordance with an embodiment of thepresent invention.

FIG. 4 illustrates an angled view of a fin-fet type semiconductor devicehaving a germanium active layer and a deep gate all-around structure, inaccordance with an embodiment of the present invention.

FIG. 5A illustrates a three-dimensional cross-sectional view of ananowire-based semiconductor structure, in accordance with an embodimentof the present invention.

FIG. 5B illustrates a cross-sectional channel view of the nanowire-basedsemiconductor structure of FIG. 5A, as taken along the a-a′ axis, inaccordance with an embodiment of the present invention.

FIG. 5C illustrates a cross-sectional spacer view of the nanowire-basedsemiconductor structure of FIG. 5A, as taken along the b-b′ axis, inaccordance with an embodiment of the present invention.

FIG. 6 includes a tunneling electron microscope (TEM) image of across-sectional view taken along the channel region of a germanium-baseddevice, and a corresponding plot of saturated current (Idsat) as afunction of gate voltage (Vg) corresponding to layers in thegermanium-based device, in accordance with an embodiment of the presentinvention.

FIG. 7 illustrates a computing device in accordance with oneimplementation of the invention.

DESCRIPTION OF THE EMBODIMENTS

Deep gate-all-around semiconductor devices having germanium or groupIII-V active layers are described. In the following description,numerous specific details are set forth, such as specific integrationand material regimes, in order to provide a thorough understanding ofembodiments of the present invention. It will be apparent to one skilledin the art that embodiments of the present invention may be practicedwithout these specific details. In other instances, well-known features,such as integrated circuit design layouts, are not described in detailin order to not unnecessarily obscure embodiments of the presentinvention. Furthermore, it is to be understood that the variousembodiments shown in the Figures are illustrative representations andare not necessarily drawn to scale.

One or more embodiments described herein are targeted to devices havinggate stacks that extend into an active region or stack, well below adepth of source and drain regions of the device. Although structurallydifferent, the resulting ability to provide leakage suppression may bedescribed as similar to an omega-fet style device. The deepgate-all-around devices described herein may be particularly suited forgermanium or III-V material based filed effect transistors (FETs) havingnanowire or nanoribbon channels. One or more embodiments described beloware directed to approaches to, and the resulting structures, reducingparasitic leakage in germanium or III-V material active layer devices.For example, one or more embodiments may be particularly effective forimproving performance in nanowire or gate-all-around devices.

We have made attempts to suppress leakage in high mobility deviceshaving wrap-around gates through the use of bottom gate isolation (BGI)structures. However, the use of BGI structures in, e.g., germanium-basednanowire or nanoribbon transistor devices may be difficult to realize.For example, although a BGI structure may be suitable for suppressingleakage, the placement of the BGI structure typically needs to extenddeep into an active region material layer or stack, which can bedifficult to integrate. Such a BGI fabrication process also requiressignificantly more complex process steps and can prove to be morecostly. Furthermore, in the case that a BGI structure is fabricated butnot to a depth sufficient for full leakage suppression, poor interfacesformed between isolation regions and germanium-based buffer layers maygenerate significant surface states causing or contributing to theparasitic leakage. Generally, regardless of how generated, the parasiticleakage can hamper transistor performance since it may degrade the offstate leakage of the device. Ultimately, such parasitic leakage canrender fabricating a low leakage germanium-based semiconductor devicedifficult to achieve.

To exemplify the concepts described herein, FIG. 1 illustrates across-sectional view of a germanium-based semiconductor device having abottom gate isolation (BGI) structure for leakage suppression. Referringto FIG. 1, a semiconductor device 100 includes a germanium (Ge) channelregion 102 grown above a silicon (Si) substrate 104 (e.g., as a portionof a silicon wafer) via silicon germanium (SiGe) buffer layers 106(e.g., a Si₃₀Ge₇₀ layer) and 107 (e.g., a Si₅₀Ge₅₀ layer) to managelattice mismatch between Ge and Si. These SiGe buffer layers 106 and 107are, however, fairly conductive in that they allow parallel conductionwithin the region underlying the channel region 102, at least within theSiGe buffer layers 106 and 107. The parallel conduction may causeparasitic leakage in the device 100, as depicted by arrow 108, from thesource region 110 to the drain region 112. It is noted that FIG. 1 alsodepicts isolation regions 114 and a gate electrode stack 116, such as ametal gate 116B and high-k gate dielectric 116A electrode stack 116. Itis to be understood that such leakage may occur even in the case of awrap-around or nanowire arrangement, where a bottom gate electrode stack116′ disposed on a bottom gate insulator (BGI) structure 120 isincluded. The BGI structure 120 may be extended to provide leakagesuppression (indicated by the X of arrow 108). However, as describedabove, this typically requires formation of BGI structure 120 deep intothe stack 106/107, as shown in FIG. 1.

In order to address the above described issues, in an embodiment, a deepgate-all-around structure is fabricated in place of a BGI structure. Forexample, in one embodiment, a bottom portion of a gate electrode isformed well below source and drain regions of the device to provideleakage suppression for the device. In a specific such embodiment, theuse of a deep gate-all-around structure in place of a BGI structurealleviates the complications and possible shortcomings associated withfabricating a BGI structure such as those described above. In anembodiment, a deep gate-all-around structure is fabricated by using adeep active region etch (such as a deep HSi etch). In one suchembodiment, the deep etch is performed up front in the fabricationscheme at shallow trench isolation (STI) fabrication. In another suchembodiment, the deep etch is performed later in the fabrication scheme,e.g., by recessing post replacement metal gate (RMG) poly removal.

In an embodiment, the use of deep gate-all-around structure leveragesthe voltage threshold (Vt) difference between Ge and SiGe layers inorder to suppress any gate capacitance (Cgate) penalty that may beassociated with using a deep gate structure. An example of the abilityto engineer the Vt to reduce such a penalty, while still being effectivefor leakage suppression, is described in greater detail below inassociation with FIG. 6. In other embodiments, the solutions describedin detail herein can readily be applied to Group III-V material systems,where similar Vt engineering may be applied to accommodate a deep gatestructure.

Thus, a deep gate structure may be fabricated for a high mobilitymaterial device. As an example, FIG. 2 illustrates a cross-sectionalview of a semiconductor device having a germanium active layer with adeep gate-all-around structure, in accordance with an embodiment of thepresent invention.

Referring to FIG. 2, a semiconductor device 200 includes a germanium(Ge) channel region 202 grown on a silicon (Si) substrate 204 (e.g., asa portion of a silicon wafer) via silicon germanium (SiGe) buffer layers206 (e.g., a Si₃₀Ge₇₀ layer) and 207 (e.g., a Si₅₀Ge₅₀ layer) to managelattice mismatch between Ge and Si. These SiGe buffer layers 206 and 207are, however, fairly conductive in that they allow parallel conductionwithin the region underlying the channel region 202, at least within theSiGe buffer layers 206 and 207. Semiconductor device 200 may alsoinclude isolation regions 214 and a gate electrode stack 216, such as agate 216B and gate dielectric 216A stack 216. A wrap-around or nanowirearrangement may be formed, where a bottom gate electrode stack 216′ isincluded, including dielectric layer portion 216A′ and gate electrodeportion 216B′. Source and drain regions 210 and 212, respectively, areincluded on either side of gate electrode stack 216, as is also depictedin FIG. 2.

Referring again to FIG. 2, the buffer layers 206 and 207 form ahetero-structure having a hetero-junction between buffer layers 206 and207. The gate electrode stack (216+216′) is disposed on and completelysurrounds a channel region of the active layer 202, and is disposed in atrench formed in the buffer layer 207 and at least partially in thebuffer layer 206. In an embodiment, the source and drain regions 210 and212 are disposed in the active layer 202 and in the buffer layer 207,but not in the buffer layer 206, on either side of the gate electrodestack (216+216′). In one such embodiment, the gate electrode stack(216+216′) is disposed to a depth in the hetero-structure (206+207)approximately 2-4 times a depth of the source and drain regions 210 and212 in the hetero-structure. In another embodiment, the gate electrodestack (216+216′) is disposed to a depth in the hetero-structure(206+207) deeper than a depth of the isolation regions 214. In anembodiment, the bottom portion of the gate electrode stack (i.e.,portion 216′) includes a portion of dielectric layer (i.e., portion216A″) that lines the trench of portion 216′, as is depicted in FIG. 2.In one such embodiment, portion 216A″ (and, hence, 216A and 216A′) is ahigh-k gate dielectric layer.

As used throughout, the terms germanium, pure germanium or essentiallypure germanium may be used to describe a germanium material composed ofa very substantial amount of, if not all, germanium. However, it is tobe understood that, practically, 100% pure Ge may be difficult to formand, hence, could include a tiny percentage of Si. The Si may beincluded as an unavoidable impurity or component during deposition of Geor may “contaminate” the Ge upon diffusion during post depositionprocessing. As such, embodiments described herein directed to a Gechannel may include Ge channels that contain a relatively small amount,e.g., “impurity” level, non-Ge atoms or species, such as Si.

Referring again to FIG. 2, in an exemplary embodiment, the substrate 204is composed essentially of silicon, the first buffer layer 206 iscomposed of silicon germanium with approximately 30% Si and 70% Ge, thesecond buffer layer 207 is composed of silicon germanium having a lowerconcentration of germanium than the first buffer layer 206 (e.g., 50% Geversus 70% Ge), and the germanium active layer 202 is composedessentially of germanium. This arrangement provides a material stackhaving a high mobility and low bandgap material for use as a channelregion. The high mobility and low bandgap material is disposed on a highbandgap material which, in turn is disposed on a medium band gapmaterial. Other stacks providing a similar bandgap arrangement may alsobe used. For example, in an embodiment, an appropriate arrangement ofgroup III-V materials in a hetero-structure may be used instead of theabove described hetero-structure based on germanium and silicongermanium layers.

In an embodiment, the source and drain regions 210/212 are disposed inthe germanium active layer 202 and in the second buffer layer 207, butare not formed as deep as the first buffer layer 206, as depicted inFIG. 2. FIG. 2 is shown generically to represent a variety of options.In a first embodiment, the source and drain regions are formed by dopingportions of the germanium active layer 202 and in the second bufferlayer 207. For example, in a specific embodiment, boron dopant atoms areimplanted into germanium active layer 202 and partially into the secondbuffer layer 207 to form source and drain regions 210 and 212. In asecond embodiment, portions of the germanium active layer 202 and thesecond buffer layer 207 are removed and a different semiconductormaterial is grown to form the source and drain regions 210/212.

Substrate 204 may be composed of a semiconductor material that canwithstand a manufacturing process and in which charge can migrate. In anembodiment, the substrate 204 is a bulk substrate, such as a P-typesilicon substrate as is commonly used in the semiconductor industry. Inan embodiment, substrate 204 is composed of a crystalline silicon,silicon/germanium or germanium layer doped with a charge carrier, suchas but not limited to phosphorus, arsenic, boron or a combinationthereof. In one embodiment, the concentration of silicon atoms insubstrate 204 is greater than 97% or, alternatively, the concentrationof dopant atoms is less than 1%. In another embodiment, substrate 204 iscomposed of an epitaxial layer grown atop a distinct crystallinesubstrate, e.g. a silicon epitaxial layer grown atop a boron-doped bulksilicon mono-crystalline substrate.

Substrate 204 may instead include an insulating layer disposed inbetween a bulk crystal substrate and an epitaxial layer to form, forexample, a silicon-on-insulator substrate. In an embodiment, theinsulating layer is composed of a material such as, but not limited to,silicon dioxide, silicon nitride, silicon oxy-nitride or a high-kdielectric layer. Substrate 204 may alternatively be composed of a groupIII-V material. In an embodiment, substrate 204 is composed of a III-Vmaterial such as, but not limited to, gallium nitride, galliumphosphide, gallium arsenide, indium phosphide, indium antimonide, indiumgallium arsenide, aluminum gallium arsenide, indium gallium phosphide,or a combination thereof. In another embodiment, substrate 204 iscomposed of a III-V material and charge-carrier dopant impurity atomssuch as, but not limited to, carbon, silicon, germanium, oxygen, sulfur,selenium or tellurium.

In an embodiment, the gate electrode of gate electrode stack 216 (andcorresponding 216′) is composed of a metal gate and the gate dielectriclayer is composed of a high-K material. For example, in one embodiment,the gate dielectric layer is composed of a material such as, but notlimited to, hafnium oxide, hafnium oxy-nitride, hafnium silicate,lanthanum oxide, zirconium oxide, zirconium silicate, tantalum oxide,barium strontium titanate, barium titanate, strontium titanate, yttriumoxide, aluminum oxide, lead scandium tantalum oxide, lead zinc niobate,or a combination thereof. Furthermore, a portion of gate dielectriclayer adjacent the channel region may include a layer of native oxideformed from the top few layers of the germanium active layer 202. In anembodiment, the gate dielectric layer is composed of a top high-kportion and a lower portion composed of an oxide of a semiconductormaterial. In one embodiment, the gate dielectric layer is composed of atop portion of hafnium oxide and a bottom portion of silicon dioxide orsilicon oxy-nitride.

In an embodiment, the gate electrode is composed of a metal layer suchas, but not limited to, metal nitrides, metal carbides, metal silicides,metal aluminides, hafnium, zirconium, titanium, tantalum, aluminum,ruthenium, palladium, platinum, cobalt, nickel or conductive metaloxides. In a specific embodiment, the gate electrode is composed of anon-workfunction-setting fill material formed above a metalworkfunction-setting layer. In an embodiment, the gate electrode iscomposed of a P-type or N-type material. The gate electrode stack 216(an correspond bottom portion 216′) may also include dielectric spacers,not depicted.

The semiconductor device 200 is shown generically to cover non-planardevices, including gate-all-around devices. Such devices are describedmore specifically below with FIGS. 3A and 3B (general non-planardevice), FIG. 4 (wrap-around fin-fet device) and FIG. 5 (nanowire-baseddevice). In all cases, a deep gate-all-around structure is integratedwith the device. The deep gate-all-around structure may be effective forsuppressing the leakage in such devices. Thus, semiconductor device 200may be a semiconductor device incorporating a gate, a channel region anda pair of source/drain regions. In an embodiment, semiconductor device200 is one such as, but not limited to, a MOS-FET or aMicroelectromechanical System (MEMS). In one embodiment, semiconductordevice 200 is a planar or three-dimensional MOS-FET and is an isolateddevice or is one device in a plurality of nested devices. As will beappreciated for a typical integrated circuit, both N- and P-channeltransistors may be fabricated on a single substrate to form a CMOSintegrated circuit. Furthermore, additional interconnect wiring may befabricated in order to integrate such devices into an integratedcircuit.

As an example, FIGS. 3A and 3B illustrate schematic top-down andcross-sectional views, respectively, of a non-planar semiconductordevice having a germanium active layer and a deep gate all-aroundstructure, in accordance with an embodiment of the present invention.

Referring to FIGS. 3A and 3B, a non-planar semiconductor device 300includes a first buffer layer 206 disposed above a substrate 204. Asecond buffer layer 207 is disposed above the first buffer layer 206. Agermanium active layer 202 is disposed above the second buffer layer207. A gate electrode stack including top portion 216 and bottom portion216′ is disposed to surround the germanium active layer 202. Source anddrain regions 210/212, and corresponding contacts 210′ and 212′, aredisposed in the germanium active layer 202 and partially in the secondbuffer layer 207, on either side of the gate electrode stack (216+216′).More specifically, in an embodiment, the source and drain regions210/212 are formed by doping portions of the germanium active layer 202and in the second buffer layer 207, as depicted in FIG. 3. As depictedin FIG. 3, semiconductor device 300 may also include isolation regions214. In an embodiment, bottom portion 216′ of the gate stack is a deepgate stack, formed well below source and drain regions 212 and 210, andacts to block a leakage path 308 from source region 210 to drain region212. It is to be understood that like feature designations of FIG. 3 maybe as described above in association with FIG. 2.

As mentioned above, embodiments of the present invention may be appliedto non-planar MOS-FETs such as fin-fet type devices having agate-all-around portion. For example, FIG. 4 illustrates an angled viewof a fin-fet type semiconductor device having a germanium active layerand a deep gate all-around structure, in accordance with an embodimentof the present invention.

Referring to FIG. 4, a non-planar semiconductor device 400 includes afirst buffer layer 206 disposed above a substrate 204. A second bufferlayer 207 is disposed above the first buffer layer 206. Athree-dimensional germanium active layer 202 is disposed above thesecond buffer layer 207. A gate electrode stack 216, including gateelectrode 216B and gate dielectric 216A, is disposed on and completelysurrounds the three-dimensional germanium active layer 202, although theportion wrapping underneath region 202 cannot be viewed from thisperspective. Source and drain regions 210/212 are disposed on eitherside of the gate electrode stack 216. Also depicted are isolationregions 214 and gate electrode spacers 440. In accordance with anembodiment of the present invention, gate electrode stack 216 is a deepgate-all-around structure which extends into first buffer layer 206.

Although depicted in FIG. 4 as being somewhat aligned with the bottom ofthe first buffer layer 206, it is to be understood that the depth of theisolation regions 214 may vary. Also, although depicted in FIG. 4 asbeing somewhat aligned with the top of the second buffer layer 207, itis to be understood that the height of the isolation regions 214 mayvary. It is also to be understood that like feature designations of FIG.4 may be as described in association with FIG. 2.

In another aspect, FIG. 5A illustrates a three-dimensionalcross-sectional view of a germanium nanowire-based semiconductorstructure, in accordance with an embodiment of the present invention.FIG. 5B illustrates a cross-sectional channel view of the germaniumnanowire-based semiconductor structure of FIG. 5A, as taken along thea-a′ axis. FIG. 5C illustrates a cross-sectional spacer view of thegermanium nanowire-based semiconductor structure of FIG. 5A, as takenalong the b-b′ axis.

Referring to FIG. 5A, a semiconductor device 500 includes one or morevertically stacked germanium nanowires (550 set) disposed above asubstrate 204. Embodiments herein are targeted at both single wiredevices and multiple wire devices. As an example, a three nanowire-baseddevices having nanowires 550A, 550B and 550C is shown for illustrativepurposes. For convenience of description, nanowire 550A is used as anexample where description is focused on only one of the nanowires. It isto be understood that where attributes of one nanowire are described,embodiments based on a plurality of nanowires may have the sameattributes for each of the nanowires.

At least the first nanowire 550A includes a germanium channel region202. The germanium channel region 202 has a length (L). Referring toFIG. 5B, the germanium channel region 202 also has a perimeterorthogonal to the length (L). Referring again to FIG. 5B, a gateelectrode stack 216 surrounds the entire perimeter of each of thechannel regions of each nanowire 550, including germanium channel region202. The gate electrode stack 216 includes a gate electrode along with agate dielectric layer disposed between the channel regions and the gateelectrode (not individually shown). The germanium channel region 202 andthe channel regions of the additional nanowires 550B and 550C arediscrete in that they are completely surrounded by the gate electrodestack 216 without any intervening material such as underlying substratematerial or overlying channel fabrication materials. Accordingly, inembodiments having a plurality of nanowires 550, the channel regions ofthe nanowires are also discrete relative to one another, as depicted inFIG. 5B.

Referring to FIGS. 5A-5C, a second buffer layer 207 is disposed above afirst buffer layer 206 which is disposed above the substrate 204. Asshown in FIG. 5B, underneath the channel region, the gate electrodestack 216 is formed into the second buffer layer 207 and partially intothe first buffer layer 206. Referring again to FIG. 5A, each of thenanowires 550 also includes source and drain regions 210 and 212disposed in the nanowire on either side of the channel regions,including on either side of germanium channel region 202. In anembodiment, the source and drain regions 210/212 are embedded source anddrain regions, e.g., at least a portion of the nanowires is removed andreplaced with a source/drain material region. However, in anotherembodiment, the source and drain regions 210/212 are composed of dopedportions of the one or more germanium nanowires 550.

A pair of contacts 570 is disposed over the source/drain regions210/212. In an embodiment, the semiconductor device 500 further includesa pair of spacers 540. The spacers 540 are disposed between the gateelectrode stack 216 and the pair of contacts 570. As described above,the channel regions and the source/drain regions are, in at leastseveral embodiments, made to be discrete. However, not all regions ofthe nanowires 550 need be, or even can be made to be discrete. Forexample, referring to FIG. 5C, nanowires 550A-550C are not discrete atthe location under spacers 540. In one embodiment, the stack ofnanowires 550A-550C includes intervening semiconductor material 580there between, such as silicon germanium or silicon intervening betweengermanium nanowires. In one embodiment, the bottom nanowire 550A isstill in contact with a portion of a second buffer layer 207. Thus, inan embodiment, a portion of the plurality of vertically stackednanowires 550 under one or both of the spacers 540 is non-discrete.

It is to be understood that like feature designations of FIG. 5A-5C maybe as described in association with FIG. 2. Also, although the device500 described above is for a single device, a CMOS architecture may alsobe formed to include both NMOS and PMOS nanowire-based devices disposedon or above the same substrate. In an embodiment, the nanowires 550 maybe sized as wires or ribbons, and may have squared-off or roundedcorners.

Furthermore, in an embodiment, the nanowires 550 may be made discrete(at least at the channel regions) during a replacement gate process. Inone such embodiment, portions of germanium layers ultimately becomechannel regions in a nanowire-based structure. Thus, at the processstage of exposing the channel regions upon a dummy gate removal, channelengineering or tuning may be performed. For example, in one embodiment,the discrete portions of the germanium layers are thinned usingoxidation and etch processes. Such an etch process may be performed atthe same time the wires are separated or individualized. Accordingly,the initial wires formed from germanium layers may begin thicker and arethinned to a size suitable for a channel region in a nanowire device,independent from the sizing of the source and drain regions of thedevice. Following formation of such discrete channel regions, high-kgate dielectric and metal gate processing may be performed and sourceand drain contacts may be added.

As described above, one or more embodiments include formation of a deepgate-all-around structure that extends into several layer of ahetero-structure stack of materials. In one such embodiment, a highmobility and low bandgap material is used as a channel region. The highmobility and low bandgap material is disposed on high bandgap materialwhich, in turn is disposed on a medium band gap material. In a specificexample involving germanium-based structures, a channel region iscomposed of essentially pure germanium. In regions other than thechannel region (where a the gate is wrapped around the germanium layer),the germanium layer is disposed on Si₅₀Ge₅₀, which has a higher ban gapthan germanium. The Si₅₀Ge₅₀ is disposed on a Si₃₀Ge₇₀ layer, with aband gap intermediate to the Si₅₀Ge₅₀ and the Ge. FIG. 6 includes atunneling electron microscope (TEM) image 600 of a cross-sectional viewtaken along the channel region of a germanium-based device, and acorresponding plot 602 of saturated current (Idsat) as a function ofgate voltage (Vg) corresponding to layers in the germanium-based device,in accordance with an embodiment of the present invention.

Referring to image 600 of FIG. 6, a germanium channel 610 is disposedabove a Si₃₀Ge₇₀ layer (fin) 612. A gate stack 614 surrounds thegermanium layer at the channel region 610. It is to be understood thatat regions other than the channel region, in one embodiment, a layer ofSi₅₀Ge₅₀ is disposed between the germanium layer and the Si₃₀Ge₇₀ layer,and the gate stack 614 is not present at those locations (e.g., at thesource and drain regions). Referring to plot 602, the Ge layer has muchhigher Idsat than the corresponding Si₃₀Ge₇₀ layer, and would be evenhigher than the Si₅₀Ge₅₀, as shown in FIG. 6. As such, althoughformation of a deep gate-all-around structure involves formation of agate stack deep into other layers of a hetero-structure stack ofmaterials, the corresponding interaction of the gate stack with thelayers other than the channel layer do not interfere with the highperformance of the fabricated device. More specifically, there is littleto no turn on in the other layers that impacts gate performance. And,perhaps most importantly, the deep gate structure can act to suppressleakage in the off-state of the device.

Thus, one or more embodiments described herein are targeted at germaniumor group II-V material active region arrangements integrated with deepgate-all-around gate electrode stacks. Such arrangements may be includedto form germanium or Group III-V material based transistors such asnon-planar devices, fin or tri-gate based devices, and gate all arounddevices, including nanowire-based devices. Embodiments described hereinmay be effective for junction isolation in metal-oxide-semiconductorfield effect transistors (MOSFETs). It is to be understood thatformation of materials such as first and second buffer layers 206/207and the germanium active region 202 may be formed by techniques such as,but not limited to, chemical vapor deposition (CVD) or molecular beamepitaxy (MBE), or other like processes.

FIG. 7 illustrates a computing device 700 in accordance with oneimplementation of the invention. The computing device 700 houses a board702. The board 702 may include a number of components, including but notlimited to a processor 704 and at least one communication chip 706. Theprocessor 704 is physically and electrically coupled to the board 702.In some implementations the at least one communication chip 706 is alsophysically and electrically coupled to the board 702. In furtherimplementations, the communication chip 706 is part of the processor704.

Depending on its applications, computing device 700 may include othercomponents that may or may not be physically and electrically coupled tothe board 702. These other components include, but are not limited to,volatile memory (e.g., DRAM), non-volatile memory (e.g., ROM), flashmemory, a graphics processor, a digital signal processor, a cryptoprocessor, a chipset, an antenna, a display, a touchscreen display, atouchscreen controller, a battery, an audio codec, a video codec, apower amplifier, a global positioning system (GPS) device, a compass, anaccelerometer, a gyroscope, a speaker, a camera, and a mass storagedevice (such as hard disk drive, compact disk (CD), digital versatiledisk (DVD), and so forth).

The communication chip 706 enables wireless communications for thetransfer of data to and from the computing device 700. The term“wireless” and its derivatives may be used to describe circuits,devices, systems, methods, techniques, communications channels, etc.,that may communicate data through the use of modulated electromagneticradiation through a non-solid medium. The term does not imply that theassociated devices do not contain any wires, although in someembodiments they might not. The communication chip 706 may implement anyof a number of wireless standards or protocols, including but notlimited to Wi-Fi (IEEE 802.11 family), WiMAX (IEEE 802.16 family), IEEE802.20, long term evolution (LTE), Ev-DO, HSPA+, HSDPA+, HSUPA+, EDGE,GSM, GPRS, CDMA, TDMA, DECT, Bluetooth, derivatives thereof, as well asany other wireless protocols that are designated as 3G, 4G, 5G, andbeyond. The computing device 700 may include a plurality ofcommunication chips 706. For instance, a first communication chip 706may be dedicated to shorter range wireless communications such as Wi-Fiand Bluetooth and a second communication chip 706 may be dedicated tolonger range wireless communications such as GPS, EDGE, GPRS, CDMA,WiMAX, LTE, Ev-DO, and others.

The processor 704 of the computing device 700 includes an integratedcircuit die packaged within the processor 704. In some implementationsof the invention, the integrated circuit die of the processor includesone or more devices, such as MOS-FET transistors built in accordancewith implementations of the invention. The term “processor” may refer toany device or portion of a device that processes electronic data fromregisters and/or memory to transform that electronic data into otherelectronic data that may be stored in registers and/or memory.

The communication chip 706 also includes an integrated circuit diepackaged within the communication chip 706. In accordance with anotherimplementation of the invention, the integrated circuit die of thecommunication chip includes one or more devices, such as MOS-FETtransistors built in accordance with implementations of the invention.

In further implementations, another component housed within thecomputing device 700 may contain an integrated circuit die that includesone or more devices, such as MOS-FET transistors built in accordancewith implementations of the invention.

In various implementations, the computing device 700 may be a laptop, anetbook, a notebook, an ultrabook, a smartphone, a tablet, a personaldigital assistant (PDA), an ultra mobile PC, a mobile phone, a desktopcomputer, a server, a printer, a scanner, a monitor, a set-top box, anentertainment control unit, a digital camera, a portable music player,or a digital video recorder. In further implementations, the computingdevice 700 may be any other electronic device that processes data.

Thus, embodiments of the present invention include deep gate-all-aroundsemiconductor devices having germanium or group III-V active layers.

In an embodiment, a non-planar semiconductor device includes ahetero-structure disposed above a substrate. The hetero-structureincludes a hetero-junction between an upper layer and a lower layer ofdiffering composition. An active layer is disposed above thehetero-structure and has a composition different from the upper andlower layers of the hetero-structure. A gate electrode stack is disposedon and completely surrounds a channel region of the active layer, and isdisposed in a trench in the upper layer and at least partially in thelower layer of the hetero-structure. Source and drain regions aredisposed in the active layer and in the upper layer, but not in thelower layer, on either side of the gate electrode stack.

In one embodiment, the channel region of the active layer has a lowerband gap than the lower layer, and the lower layer has a lower band gapthan the upper layer.

In one embodiment, the channel region of the active layer consistsessentially of germanium, the lower layer is composed of Si_(x)Ge_(1-x),and the upper layer is composed of Si_(y)Ge_(1-y), where y>x.

In one embodiment, y is approximately 0.5, and x is approximately 0.3.

In one embodiment, the channel region of the active layer, the lowerlayer, and the upper layer each is composed of a different group III-Vmaterial.

In one embodiment, the gate electrode stack is disposed to a depth inthe hetero-structure approximately 2-4 times a depth of the source anddrain regions in the hetero-structure.

In one embodiment, the device further includes isolation regionsadjacent the source and drain regions and disposed at least partiallyinto the hetero-structure.

In one embodiment, the gate electrode stack is disposed to a depth inthe hetero-structure deeper than a depth of the isolation regions.

In one embodiment, the gate electrode stack is composed of a high-k gatedielectric layer lining the trench, and a metal gate electrode withinthe high-k gate dielectric layer.

In one embodiment, the device further includes one or more nanowiresdisposed in a vertical arrangement above the active layer, and the gateelectrode stack is disposed on and completely surrounds a channel regionof each of the nanowires.

In an embodiment, a non-planar semiconductor device includes a bufferlayer disposed on a substrate. An active layer is disposed on the bufferlayer. A gate electrode stack is disposed on and completely surrounds achannel region of the active layer, and is disposed in a trench in thebuffer layer. Source and drain regions are disposed in the active layerand in the buffer layer, on either side of the gate electrode stack. Thegate electrode stack is disposed to a depth in the buffer layersufficiently below a depth of the source and drain regions in the bufferlayer to block a substantial portion of leakage from the source regionto the drain region.

In one embodiment, the channel region of the active layer has a lowerband gap than any portion of the buffer layer.

In one embodiment, the channel region of the active layer consistsessentially of germanium, and the buffer layer is composed of silicongermanium.

In one embodiment, the active layer and the buffer layer each arecomposed of a group III-V material.

In one embodiment, the gate electrode stack is disposed to a depth inthe buffer layer approximately 2-4 times the depth of the source anddrain regions in the buffer layer.

In one embodiment, the device further includes isolation regionsadjacent the source and drain regions and disposed at least partiallyinto the buffer layer.

In one embodiment, the gate electrode stack is disposed to a depth inthe buffer layer deeper than a depth of the isolation regions.

In one embodiment, the gate electrode stack is composed of a high-k gatedielectric layer lining the trench, and a metal gate electrode withinthe high-k gate dielectric layer.

In one embodiment, the device further includes one or more nanowiresdisposed in a vertical arrangement above the active layer, and the gateelectrode stack is disposed on and completely surrounds a channel regionof each of the nanowires.

In an embodiment, a method of fabricating a non-planar semiconductordevice includes forming a hetero-structure above a substrate. Thehetero-structure includes a hetero-junction between an upper layer and alower layer of differing composition. An active layer is formed abovethe hetero-structure and has a composition different from the upper andlower layers of the hetero-structure. A trench is formed in the upperlayer and at least partially in the lower layer. A gate electrode stackis formed on and completely surrounds a channel region of the activelayer, and in the trench in the upper layer and at least partially inthe lower layer. Source and drain regions are formed in the active layerand in the upper layer, but not in the lower layer, on either side ofthe gate electrode stack.

In one embodiment, forming the trench in the upper layer and at leastpartially in the lower layer is performed subsequent to removal of adummy gate structure in a replacement gate process.

In one embodiment, the channel region of the active layer has a lowerband gap than the lower layer, and the lower layer has a lower band gapthan the upper layer.

In one embodiment, the channel region of the active layer consistsessentially of germanium, the lower layer is composed of Si_(x)Ge_(1-x),and the upper layer is composed of Si_(y)Ge_(1-y), where y>x.

In one embodiment, y is approximately 0.5, and x is approximately 0.3.

In one embodiment, the channel region of the active layer, the lowerlayer, and the upper layer each are composed of a different group III-Vmaterial.

In one embodiment, the gate electrode stack is formed to a depth in thehetero-structure approximately 2-4 times a depth of the source and drainregions in the hetero-structure.

In one embodiment, the method further includes forming isolation regionsadjacent the source and drain regions at least partially into thehetero-structure.

In one embodiment, the gate electrode stack is formed to a depth in thehetero-structure deeper than a depth of the isolation regions.

In one embodiment, the gate electrode stack is composed of a high-k gatedielectric layer lining the trench, and a metal gate electrode withinthe high-k gate dielectric layer.

In one embodiment, the method further includes forming one or morenanowires in a vertical arrangement above the active layer, and the gateelectrode stack is formed on and completely surrounds a channel regionof each of the nanowires.

What is claimed is:
 1. A non-planar semiconductor device, comprising: ahetero-structure disposed above a substrate, the hetero-structurecomprising a hetero-junction between an upper layer and a lower layer ofdiffering composition; an active layer disposed above thehetero-structure and having a composition different from the upper andlower layers of the hetero-structure; a gate electrode stack disposed onand completely surrounding a channel region of the active layer, anddisposed in a trench in the upper layer and at least partially in thelower layer of the hetero-structure; and source and drain regionsdisposed in the active layer and in the upper layer, but not in thelower layer, on either side of the gate electrode stack.
 2. Thenon-planar semiconductor device of claim 1, wherein the channel regionof the active layer has a lower band gap than the lower layer, and thelower layer has a lower band gap than the upper layer.
 3. The non-planarsemiconductor device of claim 2, wherein the channel region of theactive layer consists essentially of germanium, the lower layercomprises Si_(x)Ge_(1-x), and the upper layer comprises Si_(y)Ge_(1-y),where y>x.
 4. The non-planar semiconductor device of claim 3, wherein yis approximately 0.5, and x is approximately 0.3.
 5. The non-planarsemiconductor device of claim 2, wherein the active layer, the lowerlayer, and the upper layer each comprise a different group III-Vmaterial.
 6. The non-planar semiconductor device of claim 1, wherein thegate electrode stack is disposed to a depth in the hetero-structureapproximately 2-4 times a depth of the source and drain regions in thehetero-structure.
 7. The non-planar semiconductor device of claim 1,further comprising: isolation regions adjacent the source and drainregions and disposed at least partially into the hetero-structure. 8.The non-planar semiconductor device of claim 7, wherein the gateelectrode stack is disposed to a depth in the hetero-structure deeperthan a depth of the isolation regions.
 9. The non-planar semiconductordevice of claim 1, wherein the gate electrode stack comprises a high-kgate dielectric layer lining the trench, and a metal gate electrodewithin the high-k gate dielectric layer.
 10. The non-planarsemiconductor device of claim 1, further comprising: one or morenanowires disposed in a vertical arrangement above the active layer,wherein the gate electrode stack is disposed on and completely surroundsa channel region of each of the nanowires.
 11. A non-planarsemiconductor device, comprising: a buffer layer disposed on asubstrate; an active layer disposed on the buffer layer; a gateelectrode stack disposed on and completely surrounding a channel regionof the active layer, and is disposed in a trench in the buffer layer;and source and drain regions disposed in the active layer and in thebuffer layer, on either side of the gate electrode stack, wherein thegate electrode stack is disposed to a depth in the buffer layersufficiently below a depth of the source and drain regions in the bufferlayer to block a substantial portion of leakage from the source regionto the drain region.
 12. The non-planar semiconductor device of claim11, wherein the channel region of the active layer has a lower band gapthan any portion of the buffer layer.
 13. The non-planar semiconductordevice of claim 12, wherein the channel region of the active layerconsists essentially of germanium, and the buffer layer comprisessilicon germanium.
 14. The non-planar semiconductor device of claim 12,wherein the active layer and the buffer layer each comprise a groupIII-V material.
 15. The non-planar semiconductor device of claim 11,wherein the gate electrode stack is disposed to a depth in the bufferlayer approximately 2-4 times the depth of the source and drain regionsin the buffer layer.
 16. The non-planar semiconductor device of claim11, further comprising: isolation regions adjacent the source and drainregions and disposed at least partially into the buffer layer.
 17. Thenon-planar semiconductor device of claim 16, wherein the gate electrodestack is disposed to a depth in the buffer layer deeper than a depth ofthe isolation regions.
 18. The non-planar semiconductor device of claim11, wherein the gate electrode stack comprises a high-k gate dielectriclayer lining the trench, and a metal gate electrode within the high-kgate dielectric layer.
 19. The non-planar semiconductor device of claim11, further comprising: one or more nanowires disposed in a verticalarrangement above the active layer, wherein the gate electrode stack isdisposed on and completely surrounds a channel region of each of thenanowires.
 20. A method of fabricating a non-planar semiconductordevice, the comprising: forming a hetero-structure above a substrate,the hetero-structure comprising a hetero-junction between an upper layerand a lower layer of differing composition; forming an active layerabove the hetero-structure and having a composition different from theupper and lower layers of the hetero-structure; forming a trench in theupper layer and at least partially in the lower layer; forming a gateelectrode stack on and completely surrounding a channel region of theactive layer, and in the trench in the upper layer and at leastpartially in the lower layer; and forming source and drain regions inthe active layer and in the upper layer, but not in the lower layer, oneither side of the gate electrode stack.
 21. The method of claim 20,wherein forming the trench in the upper layer and at least partially inthe lower layer is performed subsequent to removal of a dummy gatestructure in a replacement gate process.
 22. The method of claim 20,wherein the channel region of the active layer has a lower band gap thanthe lower layer, and the lower layer has a lower band gap than the upperlayer.
 23. The method of claim 22, wherein the channel region of theactive layer consists essentially of germanium, the lower layercomprises Si_(x)Ge_(1-x), and the upper layer comprises Si_(y)Ge_(1-y),where y>x.
 24. The method of claim 23, wherein y is approximately 0.5,and x is approximately 0.3.
 25. The method of claim 22, wherein thechannel region of the active layer, the lower layer, and the upper layereach comprise a different group III-V material.
 26. The method of claim20, wherein the gate electrode stack is formed to a depth in thehetero-structure approximately 2-4 times a depth of the source and drainregions in the hetero-structure.
 27. The method of claim 20, furthercomprising: forming, at least partially into the hetero-structure,isolation regions adjacent the source and drain regions.
 28. The methodof claim 27, wherein the gate electrode stack is formed to a depth inthe hetero-structure deeper than a depth of the isolation regions. 29.The method of claim 20, wherein the gate electrode stack comprises ahigh-k gate dielectric layer lining the trench, and a metal gateelectrode within the high-k gate dielectric layer.
 30. The method ofclaim 20, further comprising: forming one or more nanowires in avertical arrangement above the active layer, wherein the gate electrodestack is formed on and completely surrounds a channel region of each ofthe nanowires.